Mold for filling a truncated ball to be ground



l 1969 I F. s. .AT'WATER ,4 7

MJLD FOR FILLING A TRUNCATED BALL TO BE GROUND Original Filed April 50,1964 INV NTOR I a/mm .Anwrz-vy i W ATTORNEYS United States Patent 0.

US. Cl. 249-91 2 Claims ABSTRACT OF THE DISCLOSURE A mold is providedfor filling a truncated ball to be ground, the ball having opposed fiatend faces defining the truncated ends thereof and a bore extendingbetween said end faces. The mold is composed of a lower mold part havingan upwardly facing generally spherical cavity adapted to receive andconcentrically locate one of the end faces of the ball and an uppermolds part having a downwardly facing generally spherical cavity adaptedto engage and be concentrically located by the other of said end faces,the span between concave-surface centers of the upper and lower moldparts when so located being at least no greater than the diameter of theball, one of the mold parts having an opening for accommodating materialto be molded in both cavities and the bore.

This application is a division of my copending US. application S.N.363,889 filed Apr. 30, 1964, now Patent No. 3,299,583, which inventionrelates to the precision-finishing of truncated balls, as, for example,those which find ultimate use of the self-aligning inner ring of abearing having freedom for self-alignment within a concave sphericalouter retaining ring member.

An inner ring of the character indicated may actually be the outer-racering of an anti-friction bearing, meaning that its race accommodatesplural balls, rollers or pins, in central supporting relation with aninner-race ring. On the other hand, an inner ring of the characterindicated may provide plain-bearing journalled support for a shaft ormay be non-rotatively attached to a bracket or other part. In any event,the inner ring or truncated ball as contemplated herein has a sphericalouter surface which is truncated to define opposed end faces and whichhas a bore extending between such end faces.

In bearings of the character indicated, and particularly in certain ofthose known as plain spherical bearings where both intermittent rotationand self-alignment are to be accommodated at the outer spherical surfacethereof, it is particularly important to assure sphericity of thatsurface within very close limits. For example, sphericity must be held:0.001 inch on a three-point gage, Whether the spherical surfacediameter is one-half inch or two inches. In the past, such inner ringshave been made by the successive steps of rough-machining onautomatic-screw machines (or forged from bar or wire stock), hardening,facing to define the truncations, grinding the bore, roughgrinding andfinish-grinding the spherical surface, and finally barrel-rolling. Thisprocedure has been found to be slow and costly, and true sphericity hasbeen hard to achieve. The spherical surfaces were ground on standardoscillating grinders or on external form grinders; about 0.0002-in.stock had to be left on (after grinding) to allow for barrel-rolling,and the barrel-rolling operation required from 14 to 48 hours toaccomplish the desired cutting and burnishing operations. All in all,such prior techniques are found to be unacceptable.

It is, accordingly, an object of the invention to pro 3,437,307 PatentedApr. 8, 1969 vide an improved method of fabricating spherical rings ofthe character indicated.

A specific object is to provide such rings of superior spherical surfacecontour, using standard ball-finishing techniques as much as possible.

A general object is to meet the above objects with a method adaptable tomass-production, and having inherent capacity to reproduce to closelyheld tolerances as to sphericity, with minimum rejection rate and lowcost.

Other objects and various further features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specification in conjunction with the accompanyingdrawings. In said drawings, which show, for illustrative purposes only,preferred embodiments of the invention:

FIG. 1 is a vertical sectional view of a plain spherical bearing havingan inner ring or truncated ball finished in accordance with theinvention;

FIG. 2 is a side-elevation view of the inner ring or truncated ball ofFIG. 1, conditioned for a finishing operation of the invention, partsbeing broken to reveal a vertical section;

FIG. 3 is a sectional view through a mold of the invention;

FIGS. 4 and 5 are views similar to FIG. 3 but illustrating amodification, before and after injecting molding material;

FIG. 6 is a simplified sectional view through the spaced grooved platesof a ball-grinding machine in which the conditioned ring of FIG. 2 issupported; and

FIGS. 7 and 8 are simplified sectional views of a punchout device,before and during operation thereof.

Briefly stated, the invention contemplates the improved finishing of abearing ring or truncated ball which is a centrally bored spheretruncated at opposite ends of the bore by fiat end faces. Moldingtechniques are employed to cast a temporary core in locked relation withthe bore and integral with headed ends which are rounded to somethingjust short of the ultimate sphere to which the ring surface is to beground and lapped. These latter operations are performed by conventionalball-grinding and lapping machines. Thereafter the temporary core isremoved, and such final finishing performed as is desired.

In FIG. 1 there is illustrated a complete plain spherical bearingcomprising an inner ring or truncated ball 10 having a central bore 11extending between opposed fiat end faces 12. The outer convex surface 13of ring 10 is spherically contoured for sliding contact with and supportby the low-friction liner 14 on the inner surface of an outer bearingring 15. The liner 14 may include a fabric having Teflon fibers woventherein.

In accordance with the invention, a superior spherical surface 13 isdeveloped by casting a core 16 in locked relation with the ring 10 sothat the truncated ball or sphere of ring 10 can resemble a full sphere,for purpose of utilizing conventional gall-finishing equipment to grindand lap the desired contour of surface 13. The core 16 is shown as aone-piece casting having integral head portions 17 which are rounded tofill out the truncated end of the desired sphere. However, to avoidgrinding or lapping the core material, the spherical radial extent ofheads 17 (or at least the span S between convex-surface centers of heads17) is preferably just short of the ultimate sphere to which surface 13is to be finished. Not only does this proportioning of heads 17 assureagainst core material contaminating the ball-finishing machines, but thecore material is itself preserved against contamination and may be fullyrecovered for recycled use.

Alternative core-mold arrangements are shown in FIG. 3 and in FIGS. 4and 5, respectively, but the basic cavity requirements are bestillustrated in FIG. 3. In FIG. 3,

the mold compises upper and lower parts 20-21 which, when clamped (bymeans not shown), together define cooperating halves of a cavity, theupper half 22 of which has a molding cavity 22' which is served by aflared sprue hole 23 for introduction of molding material. The lowercavity half 24 is characterized by a region of diameter D for retentionand location of the underground truncated ball or ring 10, and acircumferentially continuous shoulder 25 provides a seat for theperiphery of one of the end faces 12. Below shoulder 25 in lower cavityhalf 24 is a bottom cavity molding part 24' which is preferably ofslightly lesser but concentrically located spherical contour, as of thelesser diameter D'. An upper shoulder 26, similar to shoulder 25, isformed in the upper cavity half 22, and above shoulder 25 the moldingcavity part 22' is preferably characterized by the lesser diameter D.Whether or not the pair of molding cavities 22'24' are strictlyspherical, the span between concave-surface centers of these halvesshould not exceed the span S alluded to in reference to FIG. 2, beingjust short of the ultimate geometrical sphere to which surface 13 is tobe finished. In practice, it has been found that highly satisfactoryresults are obtained for a lesser diameter D which is 0.005 to 0.0l-inchless than that of the ultimately lapped spherical surface 13, for ringdiameters ranging from one-half inch to two inches.

The mold of FIGS. 4 and represents the presently preferred form. Itresembles the mold described for FIG. 3 in all respects except that theseparate halves 27-28 do not come together but are really suitablycontoured plates which are spaced by an inserted ring 10. Clamping meansincluding a bolt 29 and wing nut 30 releasably hold the ring and moldparts together during a molding operation. Shoulders -26 and moldingcavities 22'24 are preferably as described for FIG. 3. In casting, asmall sprue length may remain, as suggested at 31, but this in no wayimpairs the ability to separate mold halves from the ring 10 with core16 locked thereon. The projection 31 may be simply broken or ground off,as will be understood.

In the grinding operation and in the subsequent lapping operation, thecore-locked ring 10 becomes one of a great number of balls sequentiallyfed in and processed in one of the several pairs of V-grooves in opposedsurfaces of the grinding or lapping plates. Actually, corelocked rings10 may be mixed in with steel balls in the same succession of grindingand lapping production, as long as the diameters to be finished and thesteels to be ground are essentially the same. In FIG. 6, I illustratethe core-equipped ring 10 in the grinding process, located by walls 32of one of the grooves in the upper plate 33 and by walls 34 of thecorresponding groove 35 in the lower plate 36. In the grinding process,as in the lapping process, one of the plates 33 rotates with respect tothe other, and the hundreds of balls in grooves 32-34 are subject torandom orientation as they gyrate with relative motion of the walls ofgrooves 32-34. For V-grooves inclined 90 as shown, I have observedreliably predictable superior spherical surface generation oncore-equipped rings 10 when the axial length L (FIG. 2) is in the orderof 70 percent of the diameter D, under which condition full diametralsupport of ring 10 is assured between one face 32 and the oppositeparallel face 34, regardless of orientation of ring 10. Acceptablespherical surfaces, of lesser precision at the truncation margins, havebeen obtained for L/D ratios as low as 50 percent.

The casting material for core 16 may be one of a number of availableitems, as long as its removal is complete without marring the ring 10. Ihave found standard printing-type lead, as used in linotype machines, tobe well suited to the purpose, and I have also successfully employed alow-melting point special bismuth alloy marketed under the trade nameCerrobend, being a product of Cerro Corporation, 300 Park Avenue, NewYork, N.Y.

In using lead for the core 16, I find it best to punchout the core,rather than trying to melt it out of position. A suitable punch issuggested in FIGS. 7 and 8 to comprise a base 36 having a centralopening '37 beneath a seat 38 adapted to receive and locate a ground andlapped core-equipped ring 10; the bottom of seat 38 is, of course,sufiiciently open to clear the full diameter of the adjacent core head17, and a thin shoulder 39 (analogous to shoulders 25-26, FIGS. 3 and 4)serves to vertically orient the core axis. A ram 40 of diameter tosafely clear the bore 11 is guided by means 41 on an upstanding bracket42 for reciprocation in alignment with the core axis. Initial ramcontact with the upper head 17 is followed by severance of a thin ring17' (FIG. 8) so that the body 16 and lower head 17 can be cleanlydischarged into opening 37. The final operations on the ring 10 are boregrinding and barrelrolling (tumbling) using conventional techniques asneeded.

In the use of the indicated low-melting alloy indicated, there is noneed for the punching step to remove core 16. The alloy indicated has amelting temperature of 158 F., and this is so far below any temperaturebothersome to the steel of ring 10 or its finish that mere subjection tosuch a low-melting environment is adequate, and the alloy may be fullyrecovered for recycled use.

It will be seen that I have disclosed an improved method for low-costgeneration of superior spherical convex surfaces, in mass-productionquantities. So reliable is my cast-core technique that cored rings maybe intermixed with steel balls in any given loading of a ballgrinding orball-lapping machine. The provision of corehead diameter D close to butshort of the ultimately ground spherical diameter D means that nocore-equipped ring 10 will foul an adjacent similar ring 10 sufficientlyto inhibit the normal gyrating ball rotation of conventionalball-grinding. Furthermore, the shocks and stresses of such grinding andlapping are incapable of loosening the locked engagement of core 16 toring 10, and thus no solid matter can project to impede normal ballrotation. The core material is never contacted by grinding surfaces andso the core material is neither contaminated, nor does it erode to fillor contaminate the grinding surfaces.

While the invention has been described in detail for preferred methodsand molds, it will be understood that modifications may be made withoutdeparting from the scope of the invention as defined in the claims whichfollow.

I claim:

1. A mold for filling a truncated ball to be ground, said ball havingopposed fiat end faces defining the truncated ends thereof, and saidball having a bore extending between said end faces, a lower mold parthaving an upwardly facing generally spherical molding cavity ofeffective radius at least no greater than that of the ball, acircumferentially continuous locating shoulder defining the upper limitof said cavity, said shoulder being of a diameter to receive andconcentrically locate one of said end faces with respect to said cavity,an upper mold part having a downwardly facing generally sphericalmolding cavity of effective radius at least no greater than that of theball, a circumferentially continuous locating shoulder defining theouter limit of said upper molding cavity, whereby the cavity of saidupper mold part may be concentrically located with respect to the otherend face of the ball, one of said mold parts having an opening foraccommodating material to be molded in both cavities and the bore, andreleasable holding means for retaining both mold parts in concentricallylocated relation with said end faces during a molding operation.

2. A mold for filling a truncated ball to the ground, said ball havingopposed flat end faces defining the truncated ends thereof, and saidball having a bore extending between said end faces, a lower mold parthaving an upwardly facing generally spherical molding cavity adapted toreceive and concentrically locate one of said end faces, an upper moldpart having a downwardly facing generally spherical molding cavityadapted to engage and be concentrically located by the other of said endfaces, the span between concave-surface centers of said upper and lowermold parts when so located being at least no greater than the diameterof the ball, one of said mold parts having an opening for accommodatingmaterial to be molded in both cavities and the bore, and releasableholding means for retaining both mold parts in concentrically locatedrelation with said end faces during a molding operation.

References Cited UNITED STATES PATENTS 1,936,863 1:1/ 19.33 Skillman.2,703,470 3/1955 Porter et al. 5160 3,1 14,992 12/ 1963 Reardon 51-284FOREIGN PATENTS 85 8,058 12/1952 Germany.

I. SPENCER OVERHOLSER, Primary Examiner. J. S. BROWN, AssistantExaminer.

